In the LTE Release R8/R9, the CRS (Common Reference Signal) is designed in order to measure channel quality and demodulate received data symbols, and a UE (User Equipment) can perform a channel measurement through the CRS to determine that the UE reselects a cell and switches to the target cell, and it measures the channel quality in the UE connected state, and when the interference level is relatively high, the physical layer cuts off the connection through a high-layer related wireless link connection failure signaling. In order to further improve the average spectrum utilization rate of a cell, the cell-edge spectrum utilization rate and throughput of each UE, the LTE R10 defines two reference signals respectively: CSI-RS (channel information reference signal) and DMRS (demodulation reference signal), wherein the CSI-RS is used for the channel measurement, and PMI (Precoding Matrix Indicator), CQI (Channel Quality Indicator) and RI (Rank Indicator) which the UE needs to feed back to the eNB can be calculated by measuring the CSI-RS. The DMRS can be used to make the UE transparently receive downlink data without having to know an appropriate precoding weight of the base station side, thus reducing the restrictions of a codebook on the weight at the same time of reducing the PDCCH load. In addition, the DMRS is used to support dynamically and transparently switching between the SU-MIMO and the MU-MIMO, support an interference estimation using the DMRS, which can greatly improve the interference cancellation performance of the receiving side.
New types of carriers are introduced in the late R11, and the newly introduced types of carriers mainly use the ePDCCH for transmitting control channels, so that the R10 is not compatible with the control channel region of the carriers. When originally designing the reference signal, it mainly considers using the first four OFDM symbols for the control channel region, and the first four OFDM symbols are not suitable for placing various reference signals (except of the CRS which is used for demodulating the PDCCH). For the DMRS enhancement, due to the restrictions of the control channel in design, it may affect the demodulation performance of the DMRS. In addition, because the PSS/SSS needs to be transmitted in the NCT sub-frame, in order to avoid a collision between the DMRS and the PSS/SSS, the enhancement design of the DMRS is required.